The present invention relates to optimal resource allocation in a multi-hop OFDMA wireless network with cooperative relaying.
Unlike the wired networks, wireless networks face additional challenges due to the shared nature of the wireless channel. That is, the capacities of different links in the wireless networks may be coupled as the links experience interference from each other. Thus, an optimal resource allocation strategy is required for efficient use of the network resources
Permitting simple receiver design in the frequency-selective channels, OFDMA is a major access technology for the future broadband networks. However, from the viewpoint of radio resource allocation, OFDMA yields a much more complex problem due to the existence of a large number of parallel subchannels. The difficulty is aggravated in the interference environment where multiple links can potentially share the subchannels. In OFDMA systems, the channels are subdivided in the frequency domain into subchannels, to which the given power resources must be allocated. If more than one links are to be activated in the same subchannel simultaneously, mutual interference between the links must also be considered. Also, if the cooperative relaying technique is to be employed for enhanced spectral efficiency, the power split between the cooperating relays must be determined while still accounting for the aforementioned interference issue.
In one approach, a closed-form solution was obtained for the power and spectrum allocation problem for multi-hop MIMO cooperative relay networks by approximating log(1+x) by √{square root over (x)}. It was then verified that the approximate solution is actually quite close to the exact optimal solution within a wide range of operating SNR. However, the power constraint was imposed on the network-wide total power instead of the individual power constraints per node. Also, the work assumed a flat fading channel, and hence may not be suitable for frequency selective channels that appear in wideband signaling. In another approach, the optimal power and rate control problem was solved for an OFDMA cooperative cellular network, where the mobiles can act as cooperative relays for other mobile terminals. Depending on the channel conditions perceived by the mobiles on each tone, the mobiles may opt to employ the cooperative relaying on that tone. However, since the decision is made on a tone-by-tone basis, the mobiles must be able to transmit on a particular tone at the same time as they listen on another tone.